If you inspect the blade of a traditional Japanese sword closely, you may notice various patterns in the metal. Some of these patterns resemble flowers, while others resemble streaks, lightning bolts, spirals and more.
The patterns displayed on a sword's blade are more than just aesthetic features, however. Each pattern has its own unique properties, which is traditional Japanese swordsmiths placed a great deal of emphasis on creating the right pattern. To learn more about the important of patterns in Japanese swordsmithing, keep reading.
There Was No Metallurgy...
Today, swordsmiths can use exact science to achieve their desired properties when forging and creating blades. But metalllurgy -- the science and technology of metals and their respective properties -- didn't arise until the 20th century. As a result, swordsmiths in feudal Japan had to use other methods to achieve their desired properties, such as trial and error and visual inspections of the blade's patterns.
Adding the right composition of carbon is essential when creating a sword. Without adequate carbon, the sword will be weak and unable to hold a edge. If there's too much carbon, however, it will be brittle and prone to damage upon impact. Japanese swordsmiths perfected the art of crafting swords by using the right amount of carbon. The region's tamahagane steel, for instance, contained between 3% and 4.5% carbon, allowing for superior quality swords. In order to achieve this carbon content, though, swordsmiths had to pay close attention to patterns in the metal.
Not to be confused with metallurgy, metallography is the study of the patterns in metal as well as the nature of fracture and crystal formations. Contrary to what some people believe, Japanese swordsmiths in feudal Japan didn't focus on patterns for aesthetic purposes -- not until around the 14th century at least. Rather, they inspected and studied the patterns in metal to achieve specific properties when creating swords.
Differential hardening -- the process of heating and cooling different parts of the blade at different temperatures -- often resulted in a tempering line (also known as a hardening pattern).
Another common pattern in traditional Japanese swords is a bright streak that follows the layers of the metal. Known as nioi, this pattern is revealed after polishing the blade.
photo credit: Jesus Hernandez